Device for cutting and clamping the needle thread of sewing machines



June27,1939. J, ,F HER 2,163,994

DEVICE FOR CUTTING AND CLAMPING THE NEEDLE THREAD OF SEWING MACHINES Filed Feb. 11, 1938 Patented June 27, 1939 UNITED STATES PATENT OFFICE DEVICE FOR CUTTING AND CLAMPING THE NEEDLE THREAD F SEWING MACHINES Jakob Josef Fischer, Aarau, Switzerland 4 Claims.

This invention relates to devices for cutting and clamping the needle thread of sewing machines, the device comprising a rotatable bobbin carrier acting as a thread catch and a slide block which is mounted laterally of the bobbin carrier for reciprocation toward and away from the axis of rotation of the thread catch, the former movement being opposed by the action of a resetting spring, and the slide block carrying a thread gripper arm which is pivoted thereto and controlled by means of a cam face.

In the conventional devices of this kind the cam face is arranged on a separate cam roller which influences the thread gripper arm, that is,

E the slide block through the intermediary of a complicated obstructive transmission gearing. Such an arrangement not only results in detrimentally aifecting the synchronism of movement between the device and the sewing mechanism, but also in unreliability of operation, due to the possibility of the gearing becoming damaged or obstructed. Furthermore, such arrangements can be used only for sewing machines with horizontal bobbin-holding spindles whereas in connection with the more usual vertical bobbinholding spindles they are not applicable.

According to this invention, these drawbacks are eliminated in the device by constructing the thread gripper arm as the rockable part of a 30 scissor-like pair of clamping and cutting jaws the other part of which is fixed to the slide block, and arranging the cam face directly on the bobbin carrier, in such manner, that, when the slide block assumes the operative position, the gripper arm is adapted to cooperate with the cam face for grasping the needle thread, clamping it bea tween the jaws and severing the thread.

Owing to this arrangement of the device, the thread gripper arm is actuated by the bobbin carrier directly, when it is advanced into position for operation, in which way, the necessity for any transmission gearing which is liable to cause disturbances and results in more wear is done away with. This device is of compact construction and can be used in connection with all sewing machines provided with a central bobbin irrespective of whether the bobbin-holding spindle is horizontal or vertical or whether the bobbin-holding spindle is driven directly or through the intermediary of a gearing. Moreover, the device can be included in existing machines without necessitating any other alterations than the application of a cam face to the bobbin carrier.

In the accompanying drawing an embodiment of the invention is illustrated by way of example only, in which Fig. 1 shows a sectional side elevation of the device;

Fig. 2 is a top plan view of Fig. 1;

Fig 3 is a view of the gripper arm in closing position, as seen from above;

Fig. 4 shows an end elevation of the device; and

Fig. 5 is an enlarged cross-sectional view of the clamping and cutting jaws inclosed portion.

Referring to Figs. 1 and 2 of the drawing, the numeral I designates the vertical rotatable bobbin carrier known per se of a leather sewing machine of which only those parts are shown that are necessary for a thorough understanding of the invention. The bobbin carrier l is arranged in a casing 2 above which the throat plate (not shown) for cooperation with the needle N acting on the work is situated. The bobbin carrier l in which the bobbin (not shown) is mounted is so constructed that it provides at the same time a thread catch having a groove la, which is recessed in the cylindrical circumference of the carrier and is located underneath the thread catch nose lh and serves as a cam face ending in a concaved portion lk.

Laterally on the casing 2 a bracket 3 is secured which is provided with a vertical upstanding projection 3a. The upper surface of the bracket is provided with a dove-tailed groove in which a slide block 4 is guided for reciprocation in the direction toward and away from the axis of the bobbin carrier. The slide block 4 is of rectangular shape, when seen in plan, and terminates in an inclined edge at its end facing the bobbin.

Underneath this inclined edge 4s a slightly projecting knife blade 5 is secured to the slide block in parallel relation to this edge. Longitudinally of the shorter side of the slide block a bar 6 is secured, and to the forwardly projecting end of said bar a thread gripper arm 1 is pivotally connected, the thickness of which arm is so chosen that the arm rests against the upper surface of the bracket 3, whereas the inner lower edge of this arm cooperates with the knife 5 in the manner of a pair of scissors, when the arm is rocked towards the inclined edge 48 (Fig. 3). Upon further movement the inner face of the arm cooperates with the edge 4.9 of the slide block to grip the cut-off end of the thread (Fig. 5).

A wire spring 8 which is secured to the connecting screws of the bar 6 and the outer end of which protrudes through a stud "is on the thread gripper arm "I has the tendency to rock the gripper arm counterclockwise, that is, to open the scissors. The gripper arm I is provided at its rearward end projecting beyond the pivot pin thereof with a nose In which, when bearing against a set screw 9 arranged on the slide block, secures the gripper arm I in the open position of the same. The forward end of the gripper arm, which rides on the bobbin carrier, is rounded off.

In the rear end of the slide block 4 a tap bolt I0 is screwed on the rear end of which a forked link I l is mounted, whereas a lock nut IE on the other end of the bolt serves for securing the latter in position. Between a shoulder !3 for re taining the forked link and the projection 3a of the bracket 3 a coil spring Hi surrounding the tap bolt is inserted which tends to pull the tap bolt l0 together with the slide block 4 from the full line working position into the chaindotted in operative position, in the manner of a resetting spring, by effect of the pressure acting on the shoulder l3. The gripper arm is moved out of the path of movement of the bobbin carrier in the inoperative position of the slide block, as is also indicated in chain-dotted lines in Fig. 2. To the forked link I l an arm E5 is pivoted which is actuated by a transmission linkage, an extension 3 of the bracket 3 limiting the movement of the arm [5 for exactly defining the operative position of the slide block, which can be adjusted by means of the tap bolt ii).

The gripper arm 1 projects in the operative position of the slide block 4, to which the latter has been adjusted by means of the arm IE, towards the bobbin carrier 5 so as to contact with the bottom of the groove la, as shown in Fig. 2 On rotation of the bobbin carrier the needle thread loop F is grasped by the thread catch nose UL and the gripper arm 1 is rocked towards the inclined edge 48 of the slide block until it finally rides on the outer circumference of the bobbin carrier continuing moving, so that the scissors formed by the gripper arm I and the stationary jaw 5 of the slide block 4 are completely closed, as shown in Figs. 3 and 5. In this way the clamped portion of the needle thread F behind the needle N is severed and the end thereof is clampingly held as long as the gripper arm I is maintained in the closing position by the bobbin carrier. Due to the presence of the curved end portion lie of the groove la and the edge formed by this portion at the circumference of the bobbin carrier, the gripper arm I is imparted a vigorous impulse at the moment of closing, so that even a tenacious strong thread is surely severed.

On the rotation of the bobbin carrier continuing, the thread gripper arm reenters the groove in and is opened by influence of the wire spring 8, thereby releasing the clamp-ed end of the needle thread F. Naturally, the thread is released also if the arm I5 is released immediately after the thread has been severed, whereby the slide block 4 is returned into inoperative position in which the scissors are opened by the resetting spring M.

For protecting the device from being clogged with dust and getting damaged by mechanical influences, it is covered by a protecting cover 2a.

Various changes and modifications may be made in the practice of my invention without departing from the principle or spirit thereof, by adding customary practice and established knowledge of the art to the present disclosure and the scope of the appended claims is not to be regarded as limited except as specified there- I claim:

1. Device for cutting and clamping the needle thread of sewing machines, a rotatable bobbin carrier acting as a thread catch, a slide block mounted laterally of said carrier for reciprocation toward and away from the rotation axis thereof, a resetting spring associated with said block for counteracting its movement toward said carrier, a cam controlled thread gripper member pivoted to said block for grasping the needle thread underneath the work and providing a rockable clamping and cutting jaw, a cam face provided on said carrier for cooperation with said rockable jaw for controlling the same, and a mating clamping and cutting jaw fixed to said block for cooperation with said rockable jaw as the latter is controlled by said cam face in the operative position of said block, for clamping and cutting the needle thread caught by said thread catch.

2. Device for cutting and clamping the needle thread of sewing machines, an encased rotatable bobbin carrier acting as a thread catch, a lateral bracket on the casing of said carrier provided with a dove-tailed groove, an upstanding projection on said bracket provided with a bore, a slide block mounted laterally of said carrier for reciprocation toward and away from the rotation axis thereof in said dove-tailed groove of said bracket, a shank projecting from the end of said block remote from said carrier through said bore of said projection, a shoulder on said shank, a coiled compression spring surrounding said shank between said shoulder and said projection for resetting said block away from said rotation axis, an actuating member operatively connected with said shank, a cam controlled thread gripper member pivoted to said block for grasping the needle thread underneath the work and providing a rockable clamping and cutting jaw, a cam face provided on said carrier for 00- operation with said rockable jaw, for controlling the same, and a mating clamping and cutting jaw fixed to said block for cooperation with said rockable jaw as the latter is controlled by said cam face, when said block assumes the operative position by operation of said actuating member, for clamping and cutting the needle thread caught by said thread catch.

3. Device for cutting and clamping the needle thread of sewing machines, a rotatable bobbin carrier acting as a thread catch, a slide block mounted laterally of said carrier for reciprocation toward and away from the rotation axis thereof, a resetting spring associated with said block for counteracting its movement toward said carrier, a cam controlled thread gripper member pivoted to said block for grasping the needle thread underneath the work and providing a rockable clamping and cutting jaw, provided with a rounded end, a cam face recessed in the circumference of said carrier and having a concaved rear end portion, said cam face controlling the movement of said rounded end of said rockable jaw and imparting a jerking effect thereto by action of said ooncaved end portion, and a mating clamping and cutting jaw fixed to said block for cooperation with said rockable jaw as the latter is controlled by said cam face in the operative position of said block, for

clamping and cutting the needle thread caught by said thread catch by said jerking effect.

4. Device for cutting and clamping the needle thread of sewing machines, a rotatable bobbin carrier acting as a thread catch, a slide block mounted laterally of said carrier for reciprocation toward and away from the rotation axis thereof, and terminating in an inclined edge at its front end facing said carrier a bar secured to said block and extending forwardly along the side thereof adjoining said inclined edge at the end point of the latter more removed from said carrier, a stop provided on said front end of said carrier substantially at the level of said bar, a resetting spring associated with said block for counteracting its movement toward said carrier, a cam controlled thread gripper member pivting jaw flxed to said block for cooperation with 10 said rockable jaw as the latter is controlled by said cam face in the operative position of said block with said nose abutting said stop for limiting said operative position; for clamping and cutting the needle thread caught by said thread 15 catch.

JAKOB JOSEF FISCHER. 

